1. Field of the Invention
The present invention relates to a portable power supply and, more specifically, to a portable power supply to be connected to electronic devices such as a handy game machine (commercially available by the name of "GAME BOY") employing dot matrix liquid crystal display screen.
2. Description of the Background Art
Generally, a power supply for supplying power to various electric devices and electronic devices such as electric tools, video cameras and so on has a box-shaped body case containing batteries.
For example, Japanese Utility Model Laying Open No. 60-855 discloses a portable battery case. In this battery case, charging is done with the case body containing storage batteries attached to a charger, and after the charging is completed, it is detached from the charger, and a holder body having a hook is engaged so that power can be supplied to an electronic device while it is carried. Sometimes, such battery case is used incorporated in or attached to the body of the electronic device to which the power is supplied. A storage battery is charged by connecting the same to a charger provided separately from the battery case, as shown in Japanese Utility Model Laying Open No. 56-61973 and in Japanese Utility Model Laying Open No. 56-166664, for example.
Japanese Utility Model Laying Open No. 57-161768 discloses a packed power supply which is capable of both supplying power to electronic devices and of being charged from a commercial power source. The packed power supply contains a storage battery and a step-down transformer for supplying charging power to the storage battery. In charging, plugs are exposed to be inserted into receptacles, and after charging, the packed power supply is used incorporated in the body of the electronic device. Therefore, the packed power supply cannot supply power to an electronic device or the like while it is being charged. In addition, since power supply to an electronic device is done when the power supply is incorporated in or attached to the device, a space for accommodating the packed power supply must be provided in the electronic device, which prevents reduction in size of the electronic device.
In view of the foregoing, U.S. Pat. No. 3,919,615 discloses a power belt for carrying a portable power supply adapted to supply power to an electronic device while repeatedly charging the storage battery. The portable power supply comprises an input terminal which is connected to a commercial power source, an output terminal which is connected to an electronic device such as a video camera, the storage battery to be charged, and a charger, and the storage battery and the charger are electrically connected to each other through an external connecting cord. Therefore, the use of the portable power supply with the power supply attached to a human body is not very safe, since electric contact and the like between the storage battery and the connecting code are exposed.
In an inverter unit 80 of the above described power belt, a voltage lowering portion such as a step-down transformer or a transistor inverter is provided for supplying charging power to the storage battery by lowering the voltage of the commercial power source. It may be possible to attach the inverter unit to a human body while the power supply is connected to a commercial power source to charge the storage battery, enabling use of the electronic device. However, if the charging or power supply to the electronic device is carried out with the body case attached to one's body, the voltage lowering portion is considerably heated by the operation. Therefore, the user may feel uncomfortable or anxious, since his body (waist) touching the rear surface of the body case is heated by the heat radiation therefrom. The heat caused by the voltage lowering portion becomes more and more conspicuous as the volume of the body case becomes smaller and smaller, when a transistor inverter is used for the voltage lowering portion in order to minimize the portable power supply.
A portable power supply as described above comprises an input portion connected to a commercial power source, and an output portion for supplying power of a storage battery to an electronic device or the like. Such a power supply is often used and treated while it is carried. Accordingly, when the power supply happens to fall on the floor, for example, the input portion or the output portion provided outside the body case may be damaged or deformed by the shock at the time of falling. This may cause troubles in connecting the power supply to the commercial power source or to electronic devices.